Plateable structural adhesive for cyanate ester composites

ABSTRACT

An adhesive is provided for bonding cyanate ester composite parts together which is also plateable with metal once chemically etched. The adhesive comprises a polymeric matrix and a filler of cyanate ester polymer. The polymeric matrix comprises at least one polyepoxide resin and a curing agent, while the cyanate ester polymer filler is present in the adhesive as a powder. In practice, the present adhesive is applied to the surface of cyanate ester composite articles to be bonded and is allowed to cure at room temperature. Thereafter, the surface of the assembly is chemically etched and then plated with metal. The present adhesive enable the complete coverage of the cyanate ester composite assembly with the plated metal, including the adhesive bondlines. A cyanate ester resin structure assembled with the present adhesive composition may, upon plating, replace certain metallic components in such applications as aircraft, spacecraft, and automobiles given its highly conductive and comprehensive metallic coating.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 08/549,139 filed Oct. 27,1995, U.S. Pat. No. 5,780,581. The present application is related toapplication Ser. No. 08/339,380, filed on Nov. 14, 1994,now abandonedupon filing continuation application Ser. No. 08/638,694 on Apr. 26,1996 now U.S. Pat. No. 5,739,268 and application Ser. No. 08/549,141,filed on Oct. 27, 1995 and co-pending herewith. The former is directedto a method for preparing the surface of cyanate ester polymercomposites for subsequent plating with metal. The method of preparationincludes a step of contacting the surface with a preheated solutioncomprising a quaternary ammonium hydroxide or a primary amine. Thelatter is directed to a metal-filled adhesive for bonding cyanate estercomposites, with both the cyanate ester composites and the metal-filledadhesive being plateable with strong metal adhesion upon treatment by asurface etching process such as that recited in the above-referencedapplication Ser. No. 08/339,390 U.S. Pat. No. 5,569,493.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to bonding cyanate ester composites toone another, and more particularly, to an adhesive that bonds cyanateester composites while also being plateable with strong metal adhesionupon treatment by a surface etching process.

2 Description of Related Art

Metals are commonly employed in manufacturing because they offer highdegrees of ductility and strength as well as high conductivity. However,metals are generally heavier than other common materials like plasticsand non-metallic composites, such that the positive characteristicsattributable to metals often come at the cost of increased productweight. Increased product weight is particularly a concern in industriesmanufacturing vehicles of transport such as automobiles, aircraft, andspacecraft, as well as payloads of such vehicles, given that increasedweight adversely affects fuel economy. Moreover, metals typically have ahigher coefficient of thermal expansion than non-metallic composites,such that metals exhibit more dimensional change given temperaturedifferentials.

Accordingly, these industries have increasingly incorporatednon-metallic, lighter-weight materials such as plastics into automobilesand aircraft in an effort to economize fuel and to maintain dimensionalstability. However, plastics are not universally suitable as substitutesfor metals. For example, while plastics offer high degrees of ductilityand strength, plastics are relatively nonconductive materials. Thus,plastics cannot supplant metals used as electrical, thermal, ormicrowave conductors.

It is therefore desirable to plate a metal coating onto plastic, therebysimultaneously realizing the benefits of both metals and plastics. Morespecifically, metal plating on plastic materials allows the use of theselighter-weight plastic materials for the bulk of components andminimizes the amount of metal required to achieve a highly conductivesurface. Of particular interest is metal plating on cyanate esterpolymer composites of cyanate ester resin and graphite fiber, since suchcomposites have certain unique advantages that make them very useful forspecific applications, such as applications in communicationsspacecraft. Specifically, cyanate ester polymer composites can beformulated in ways that make them very resistant to even minutedimensional changes that would otherwise occur as a result oftemperature changes or the absorption and desorption of moisture in thepresence of air.

Two methods have been developed by which a cyanate ester compositesurface may be treated in preparation for the subsequent plating ofmetal, both of which are the subjects of previously-filed applicationsassigned to the present assignee. An application entitled "Preparationof Cured Cyanate Ester Resins and Composites for Metal Plating" (Ser.No. 08/339,390, filed Nov. 14, 1994 and co-pending herewith, recitestreating the surface of cyanate esters polymers and composites with apreheated solution of an alkali metal salt of an alkoxide to achievegreater adhesion between the surface and subsequently-plated metals. Asecond application filed on even date therewith and entitled"Preparation of Cyanate Ester Polymers and Composites for Metal Plating"(Ser. No. 08/339,380) recites treating the surface with a preheatedsolution comprising a quaternary ammonium hydroxide or a primary amine.

The above-described surface treatment methods achieve greater adhesionfor cyanate ester polymer composites by chemically etching the compositesurfaces. Chemical etching textures the composite surfaces, therebyproviding mechanical anchoring sites for the plating of metal such thatthe metal adheres to the composite. Scanning electron micrographs haverevealed that surface texturing derives from microcracking in thecyanate ester resin that is wedged between the stiff graphite fibers ofthe composite.

Adhesion between cyanate ester composites and subsequently-plated metalsis further improved by practicing the invention described in anapplication entitled "Cyanate Ester Films that Promote Plating Adhesionto Cyanate Ester Graphite Composites" (Ser. No. 08/507,178, filed onJul. 26, 1995, and co-pending herewith. That application recitesimproving the adhesion between cyanate ester composites and asubsequently-plated metal by applying a film of cyanate ester resin tothe composite surface prior to surface etching. The cyanate ester resinfilm provides a homogenous surface upon which to obtain uniformity ofadhesion between the cyanate ester resin composite and asubsequently-plated metal. In the absence of a cyanate ester resinlayer, the inconsistent distribution of graphite (or othercomposite-forming material) across the surface of the cyanate esterresin composite leads to variability in adhesiveness with asubsequently-plated metal.

While the above-described surface treatment methods provide thenecessary surface texturing for subsequently plating a metal onto thetreated composite surface, structural adhesives presently available tobond cyanate ester composites together plate poorly following suchtreatments. Cyanate ester composite articles are often pieced togetherto form complicated structures, since it would be impractical bothtechnically and economically to fabricate complicated structures as asingle piece. Since presently-available structural adhesives fail tosatisfactorily plate by the same processes used to prepare their cyanateester composite adherends, structures assembled from cyanate estercomposite articles are not comprehensively plated with metal. Morespecifically, there are delineations in the metal plating at the exposedbondlines. Discontinuities in the plating of composite structurespreclude their use in certain sensitive applications, such as satellitemicrowave circuitry.

Presently, structural adhesives available to bond cyanate estercomposite articles together include cyanate ester adhesives andepoxy-based adhesives. While certain commercially-available cyanateester adhesives may be successfully prepared for metal plating by theabove-described surface etching processes, these adhesives require curetemperatures greatly exceeding 120° C., at which graphite fiberreinforced cyanate ester composites warp. In contrast, while certaincommercially-available metal-filled epoxy adhesives cure at roomtemperature to bond cyanate ester composites without warpage, theseadhesives either plate poorly following the above-described surfaceetching treatments or, upon plating, exhibit unacceptably low lap shearand peel strengths. For example, aluminum-filled epoxy adhesives (suchas Ciba Geigy's RP4036 with RP1500 hardener) fail to plate properlyfollowing treatment by the above-described etching processes without anadditional special activation step. Commercially-available silver-filledepoxy adhesives contain large amounts of silver filler to achieveelectrical conductivity; as a result, metal subsequently plated ontothese adhesives (following surface etching) suffers from low lap shearand peel strengths because of the large amount of filler material.

Thus, a need remains for an adhesive that develops strong bond joints tocyanate ester composites while also being capable of developing strongadhesion to a subsequently-plated metal given surface texturingtreatments that are performed simultaneously on the adhesive and itscomposite adherends. The adhesive must be easy to apply and readilycurable at temperatures low enough such that the adherend cyanate estercomposite parts are not warped. Finally, the adhesion achieved betweenthe exposed bondline of the adhesive and the subsequently-plated metalmust be uniform and reproducible, since a single plating failure in anapplication such as a satellite microwave circuit can be economicallycatastrophic.

SUMMARY OF THE INVENTION

In accordance with the present invention, an adhesive is provided suchthat, when bonding cyanate ester composite articles together, both thecomposite articles and the adhesive bondline are similarly plateablewith metal following surface texturing. The adhesive of the inventioncomprises a polymer mixture and a filler, with the polymer mixturecomprising at least one polyepoxide resin and a substantiallystoichiometric amount of curing agent and the filler comprising curedcyanate ester polymer.

In practice, the adhesive of the invention is formulated by providingthe cured cyanate ester polymer in powder form and mixing the curedcyanate ester polymer powder with the polymer mixture to form athoroughly wetted mass. The adhesive is in the form of a flowable pastethat is curable at room temperature. To employ the adhesive in thepractice of the invention, one simply applies the adhesive to thesurface of at least one of the cyanate ester composite articles to bejoined and then secures the articles as a mated assembly with theadhesive between and in contact with the articles to bonded. Theadhesive then cures at room temperature, thereby bonding the cyanateester composite articles to one another without exposing the articles toelevated temperatures and the risk of warpage.

The adhesive of the invention may be plated with metal to the sameextent possible with cyanate ester polymer composites. Moreparticularly, once the cyanate ester polymer composites are bonded withthe present adhesive, the entire assembly may then be etched using asurface texturing technique and subsequently plated with metal. Theexposed bondlines of the present adhesives are etched and plated alongwith the cyanate ester composite articles.

Accordingly, the adhesives of the invention allow industry to securelybond together cyanate ester composite articles such that the exposedbondlines likewise are successfully plated with metal. As such, complexstructures boasting the light weight and dimensional stability of curedcyanate ester polymer composites may be assembled from separate partsmade of cured cyanate ester resin composites and thereafter etched andplated as a whole. Thus, the assembled cyanate ester compositestructures exhibit complete coverage by the plated metal withoutundesirable delineation by unplated bondlines.

The adhesive and methods of the present invention are expected to have apositive economic impact on the automotive, aircraft, and spacecraftindustries. By enabling industry to confidently assemble cyanate estercomposite parts into wholly plateable structures, industry need notmanufacture complex structures as a single piece, which would betechnically and economically challenging if not impossible. Thus, theadhesive of the invention enables the replacement of complex metalstructures with lighter-weight, dimensionally-stable assembles made ofcured cyanate ester resin composite articles, thereby reducing totalproduct weight and achieving greater fuel efficiency in vehicles oftransport.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The adhesive of the present invention develops strong bond jointsbetween cyanate ester composites and is also plateable with strong metaladhesion when etched along with its cyanate ester adherends. Moreover,the adhesive is curable at room temperature so that the cyanate estercomposite adherends are not warped by an elevated cure temperature, andthe adhesive is rigid and dimensionally stable. The adhesive comprises apolymeric matrix and a filler of cyanate ester polymeric material, asdescribed in greater detail below. All told, the present adhesivesenable industry to assemble cyanate ester composite parts into complexstructures having unobtrusive, plated bondlines.

The adhesives of the present invention are specifically designed to bondcyanate ester resin composites together, with the composites comprisinga cyanate ester resin and a fiber such as graphite or fiberglass.Examples of commercially-available cyanate ester resins that form partof composites benefited in the practice of the invention include, butare not limited to, cyanate ester resin RS12 available from YLA, cyanateester resins BTCY-1, EX-1502, and EX-1515 available from Bryte, andcyanate ester resin 954-2A available from Fiberite. Examples ofcommercially-available graphite fibers that form part of cyanate esterresin composites benefited in the practice of the invention include, butare not limited to, XN-80 carbon fibers available from Nippon Granoc,K13B from Mitsubishi, and M55J from Toray. Further, rather than graphiteor fiberglass, the composite may comprise Kevlar™ fibers, which arearomatic polyamide fibers that are commercially available from DuPont.

The composition of the present adhesive is based on the use of acombination of selected polyepoxide resins, curing agents, and fillerswhich will provide a room-temperature curable product that providesstrong bonds between cyanate ester composite materials while beingplateable with metal following surface texturing. The selection of eachof these components is critical in obtaining an adhesive with thedesired properties. The purity of the components employed in thepractice of the invention is that employed in normal commercial practicein the formulation of cyanate ester resin components.

The polymeric matrix of the present adhesives is composed of at leastone polyepoxide resin and a curing agent. The polyepoxide resinssuitably employed in the practice of the invention preferably have aviscosity not exceeding 30,000 cP at room temperature, yet areclassified as "rigid" epoxy resins. Rigid epoxy resins are defined asepoxy resins having a Shore D measurement exceeding about 75 when curedwith diethylene triamine ("DETA"). However, the adhesives of theinvention are not so limited and may employ flexible epoxy resins havingShore D measurements of less than 75 when cured with DETA, dependingupon the particular application.

Examples of classes of polyepoxide resins suitably employed in thepractice of the invention include, but are not limited to, thediglycidyl ether of Bisphenol A and diglycidyl ether of Bisphenol F.Specifically, polyepoxide resins suitably employed in the practice ofthe invention include, but are not limited to, the following resinswhich are all commercially available from Shell Chemical Company ofHouston, Tex.: (1) a mixture comprising 11% butyl glycidyl ether and 89%diglycidyl ether of Bisphenol A, which has an epoxy equivalent weight ofabout 175 to 195, and is commercially available under the tradedesignation EPON 815 and (2) diglycidyl ether of Bisphenol A, which hasan epoxy equivalent weight of about 185 to 192, and is commerciallyavailable under the trade designation EPON 828. Preferably, EPON 815 andEPON 828 are employed in the practice of the invention. Additionally, B.F. Goodrich 1177 may also be suitably employed; this resin is adiglycidyl ether of Bisphenol A that is commercially available as atwo-component mixture with a curative.

A mixture of suitably employed polyepoxide resins may be employed in thepractice of the invention.

The curing agents employed in the present invention are chosen to rendera cure at room temperature with the selected polyepoxide resins. Theprimary curing agent component is selected from the class of aliphaticpolyamines. Examples of suitably-employed aliphatic polyamines includetriethylenetetramine ("TETA"), tetraethylenepentamine ("TEPA"),diethylenetriamine ("DETA"), and N,N-diethyletlanolamine ("DEEA"), allof which are commercially available from E. V. Roberts. TETA and TEPAare polyamines containing both primary and secondary amine groups. TEPAis preferred in the practice of the invention to TETA, which is morevolatile. However, as demonstrated in the examples below, neither TEPAnor TETA cure well in air without being against any surfaces, with anair cure resulting in a tacky surface. TEPA provides a less tackysurface than TETA. The primary curing agent may be represented by asingle aliphatic polyamine or by a combination of aliphatic polyamines.

In addition to a primary curing agent of aliphatic polyamine(s), asecondary curing agent may be employed in the practice of the invention.The secondary curing agent may be selected from the group ofcatalytic-type curing agents, which serve reduce surface tackiness inthe adhesive. Examples of suitably-employed catalytic-type curing agentsinclude, but are not limited to, tris (dimethyl-amino) methyl phenol,such as commercially available from Air Products under the tradenameAncamine K54, and amine-terminated butadienenitrile rubber, such ascommercially available from B. F. Goodrich under the tradename ATBN1300×6. Ancamine K54 is the preferred secondary curing agent in thepractice of the invention.

The amount of curing agent employed in the polymeric matrix ispreferably in stoichiometric proportion relative to the polyepoxideresin employed. In general, the amount of curing agent may be variedabout ±15 percent from stoichiometry, with little adverse effect on thefinal product. The severity of adverse effects deriving from employingmore or less than the exact stoichiometric amount of curing agentdepends upon the functionality of the ingredients employed (e.g.,trifunctional epoxy resins fare better than difunctional epoxy resins).

The filler component of the present adhesive composition comprises curedcyanate ester plastic material which has been ground to a powder. Anycyanate ester polymer may be employed in the practice of the invention,but the following four are preferred in the order listed: BTCy-1,E083194-1M, EX-1502, and EX-1515, all of which are commerciallyavailable from Bryte Technologies of Milpitas, Calif. The cyanate esterpolymer may be used with or without fiber reinforcement, such asprovided by graphite fibers such as XN-80 from YLA and T300 fromFiberite. Regardless of the type of cyanate ester polymer or compositeemployed as the filler component, it must first be cured in the practiceof the invention, which is accomplished in accordance with manufacturerinstructions. The cured cyanate ester polymer material is preferablyground to a powder and screened such that an average particle size ofless than 25 μm is achieved. To render the cured cyanate ester polymermaterial more brittle in preparation for grinding, the cured polymermaterial is preferably frozen (e.g., in liquid nitrogen) prior togrinding.

The cyanate ester polymer filler serves to provide mechanical anchoringsites for a subsequently-plated metal. More particularly, chemicaletching processes used to prepare cyanate ester polymer composites forplating actually texturize the surfaces such that there are mechanicalanchoring sites for the plating of metal. In short, the chemical etchingprocesses etch away cyanate ester polymer to produce such anchoringsites. When cyanate ester polymer filler is incorporated into anepoxy-based adhesive and the adhesive is subsequently subjected tochemical etching processes for cyanate ester composites, the cyanateester polymer filler etches away faster than the epoxy matrix, therebycreating the desired texture and mechanical anchoring sites. Notably, ifthe surface irregularities created by etching are too coarse, theplating will appear coarse, which is an undesirable characteristic.Therefore, it has been determined experimentally that surface textureand resulting plating adhesion for the cured adhesives are optimized byemploying filler particle sizes not exceeding about 25 μm, referring tothe diameter of the nominally spheroidal particles comprising thecyanate ester powder.

The filler component should represent at least 15 vol % of the adhesivecomposition but should not exceed 50 vol %. If insufficient cyanateester polymer filler is employed, too few mechanical anchoring siteswill be created with surface texturing processes and there will be pooradhesion with a subsequently-plated metal. On the other hand, if anexcessive amount of cyanate ester polymer filler is employed, there willbe insufficient polymeric matrix to provide a strong bond betweencyanate ester composite articles.

Optional components for the present adhesive composition include fineceramic powders having an average particle size of about 5 μm to lowerthe coefficient of thermal expansion. Other optional components includeUV stabilizers, antioxidants, and various other processing aids such aswetting agents, anti-foaming agents, an dispersing agents, all of whichare known and commonly used in the art. The processing aids arepreferably employed at a concentration of less than about 5 wt % of thetotal adhesive composition. These optional additives cannot be addedindiscriminately, since any change to the surface chemistry can changethe plateability of the adhesive composition.

The adhesive of the present invention is formulated by mixing the liquidpolyepoxide resin(s) with the dry ingredients, namely the curingagent(s) and the filler component(s), in their appropriateconcentrations until the dry ingredients are thoroughly wetted.Preferably, the dry ingredients are milled into the polyepoxide resincomponent, for example, using a 3-roll mill. Milling achieves a goodblend of resin and curative so that the resulting adhesive is uniform incomposition and therefore exhibits higher overall quality. Once the dryingredients are thoroughly wetted, air is removed from the adhesivemixture by further mixing it under vacuum. The resulting composition hasthe consistency of a flowable paste. The present adhesives may either beused promptly upon formulation or, the more likely scenario, are frozento extend their storage life for several weeks. If frozen, the presentadhesives may be thawed as needed.

In practice, the present adhesives are applied to at least one of thesurfaces of the cyanate ester composite articles to be bonded together.Application may be accomplished with a brush or spatula or any toolcapable of spreading the paste-like consistency of the adhesives. Theadhesives are preferably applied to a thickness of at least about 0.002to 0.010 inch. Once the adhesive has been applied, the cyanate estercomposite articles to be bonded are pressed together in a mated assemblywith the adhesive therebetween. The mated assembly is then preferablyclamped in place to avoid any relational movement between the assembledarticles until the adhesive has cured, which typically occurs within 24hours at room temperature, or at a temperature within the range of about70° and 110° C. Upon cure, the present adhesive composition forms astrong, rigid bond between the cyanate ester composite articles.

The manner in which a cure of cyanate ester composite articles isachieved prior to application of the present adhesive and bonding formsno part of this invention, with a typical curing process being conductedin an autoclave at a temperature ranging from about 250° to 350° C. Thelength of time required to achieve a cure depends entirely upon thespecific cyanate ester composite being cured, while the length of timerequired to ramp to the cure temperature depends upon the thermal massand emissivity of the part. Notably, the cyanate ester compositearticles may be further prepared for plating by depositing on thesurface thereupon a layer consisting essentially of cyanate ester resinprior to curing, bonding, and etching. This procedure is recited in anapplication assigned to the present assignee and entitled "Cyanate EsterFilms that Promote Plating Adhesion to Cyanate Ester GraphiteComposites" (Ser. No. 08/507,178 filed on Jul. 26, 1995 and co-pendingherewith. Once a layer of uncured cyanate ester is in place, thecomposite and its resin layer are simultaneously subjected to the curingprocess, which securely fuses the composite and its resin layertogether. Preferably, a cyanate ester resin film having a thickness ofabout 0.001 inch is applied to the composite surface to achieve a filmof resin having a thickness of about 1 to 2 μm on the surface, sincemuch of the cyanate ester resin from the film diffuses into the laminateduring curing.

Once the adhesives of the present invention have been employed to forman assembly of cyanate ester composite articles, the entire assembly maythen be subjected to chemical etching processes in preparation for asubsequent metal plating. The manner of etching the composite andbondline surfaces forms no part of the present invention and may beaccomplished in any appropriate etching process. Preferably, the surfaceis etched in accordance with the method disclosed in the applicationentitled "Preparation of Cyanate Ester Polymers and Composites for MetalPlating" (Ser. No. 08/339,380), which recites treating the surface ofcyanate ester polymer composites with a preheated solution comprising aquaternary ammonium hydroxide or a primary amine. In general, the methoddisclosed in this related application, discussed below in greaterdetail, involves immersing the surface of the cured cyanate ester resincomposite to be metal-plated into the preheated solution and rinsing thesurface with water and/or alcohol upon removal from the solution.

Accordingly, the first step in pretreating the cyanate ester resincomposite assembly involves immersing the assembly surface in apreheated etching solution comprising a quaternary ammonium hydroxide ora primary amine. In the event that a quaternary ammonium hydroxide ischosen to etch the composite, the surface of the cured resin compositeis placed in contact with a preheated solution comprising a quaternaryammonium hydroxide (R₄ --NOH) where R may be represented by an alkylgroup, aryl-alkyl group, a hydroxy-alkyl group, or an alkoxy-alkylgroup. More specifically, the quaternary ammonium hydroxide may berepresented by such compounds as tetrabutylammonium hydroxide,benzyltrimethyl-ammonium hydroxide, tetramethylammonium hydroxide,tetraethylammonium hydroxide, tetrapropylammonium hydroxide,tetrapentylammonium hydroxide, tetrahexylammonium hydroxide, and(2-hydroxyethyl) trimethyl ammonium hydroxide, which is also known ascholine. Preferably, the alkyl groups employed have chain lengthsranging from one to six carbon atoms. Each of these quaternary ammoniumhydroxide compounds is commercially available. A quaternary ammoniumhydroxide solution is effective at a concentration ranging from aslittle as 4 wt % but may be employed without dilution.

In the event that a primary amine is used to etch the cyanate esterresin composite assembly, the surface of the assembly is placed incontact with a preheated solution comprising a primary amine (R--NH₂)where R may be represented by an alkyl group, an aryl-alkyl group, ahydroxy-alkyl group, or an alkoxy-alkyl group. More specifically,suitably-employed primary amines must have a boiling point ("BP")significantly higher than the operating temperature of the solution,which is preferably maintained at a temperature between 80° C. and 125°C. Examples of suitable primary amines include triethylenetetraamine(BP˜=266° C.), hexanediamine (BP˜=204° C.), octylamine (BP˜=175° C.),and ethylenediamine (BP ˜=118° C.). Other primary amnines believedsuitable include diethylenetriamine, tetraethylenepentaamine,1,7-diaminoheptane, 2-methyl-1,5-pentanediamine, 1,5-pentanediamine,1,3-propanediamine, 1,2-propanediamine, 1,4-butanediamine, pentylamine,hexylamine, heptylamine, octylamine, nonylamine, and decylamine. Each ofthese primary amines is commercially available and is preferablyemployed without dilution from its commercially-available concentration.Secondary and tertiary amines are not suitable because they either reactextremely slowly or not at all. Notably, triethylenetetraamine has bothprimary and secondary amine groups, but the secondary amine groups arenot believed to contribute significantly to texturizing the cyanateester resin composite surface.

A two-step etching process may be employed using preheated solutionscomprising primary amines. More particularly, the cyanate ester resincomposite assembly is first immersed in a relatively aggressive primaryamine and then immersed in a relatively less aggressive primary amine.Examples of relatively aggressive primary amines are those primaryamines within the class of short-chain primary diamines.

Regardless of whether the preheated solution comprises a quaternaryammonium hydroxide or a primary amine, the preheated solution may alsooptionally comprise an additional solvent, such as ethoxyethanol,propanediol, and pyrrolidone, among others. Such solvents serve variouspurposes, including to dissolve decomposition products; to dilute thepreheated solution; to swell the undecomposed portion of the resin; andto smooth the surface of the resin.

The temperature of the preheated solution is preferably maintained at atemperature within the range of about 80° to 125° C., with the mostpreferable temperature depending upon the particular cured cyanate esterresin composite being treated. If the temperature is too low, theadhesion achieved may be less than optimal. On the other hand, if thetemperature is too high, the chemical reaction rate is greatlyaccelerated so that the process may be uncontrollable. In reality, theupper temperature limit is often determined by the refluxing temperatureof the solution. It is preferable that the process temperature be wellbelow the boiling point of the solution.

To perform the chemical etching treatment, the surface of the cyanateester composite assembly is immersed in the preheated solution for atleast 10 seconds. Preferably, the assembly remains immersed for a periodof time ranging from 10 seconds to 20 minutes. An immersion of less than10 seconds does not adequately prepare the surface for metal plating,while an immersion lasting more than 20 minutes dissolves an excessiveamount of resin, resulting in loss of adhesion. At the conclusion of theimmersion step, the cyanate ester resin composite assembly is removedfrom the preheated solution, rinsed, and dried. The assembly surface maybe rinsed with water (preferably deionized), an organic solvent, or acombination thereof, with the purpose of rinsing being to smooth thesurface and to partially redissolve decomposition products. Solventsthat may be employed as rinsing agents include, but are not limited to,those common organic solvents listed above for use in the preheatedsolution. The assembly surface may be rinsed with room-temperature waterand/or organic solvent from a beaker for 5 minutes or more, buttypically 30 seconds of rinsing is sufficient. The etched surface isthen dried, which is preferably accomplished either by allowing theresin surface to air-dry at room temperature or by blowing the surfacedry with a stream of nitrogen. Once dry, the cyanate ester resincomposite assembly surface, including any exposed bondlines of thepresent adhesive composition, is fully prepared for metal plating andmay be plated at any time for up to one week.

The method used to perform the metal plating to the cyanate ester resincomposite assembly, having been prepared for plating by chemicaletching, does not form part of the invention and may be accomplished byany of the conventional processes known in the art, such aselectroplating, electroless chemistry, and sputtering. One traditionalmethod entails four basic sequential steps and utilizes both electrolesschemistry and electroplating. First, the assembly surface is treatedwith an acidic solution of palladium chloride and stannous chloride.This acidic solution is available commercially; for example, it is soldunder the trade name Cataposit 44 by Shipley. Second, the assemblysurface is treated with a hydrochloric acid accelerator, such ascommercially-available Accelerator No. 19 from Shipley. Third, theassembly surface is treated with either a nickel or copper electrolessplating solution. One electroless nickel plating solution is prepared bycombining 150 ml of Solution A with 100 ml of Solution B, both of whichare commercially available from Allied Kelite, and then diluting the 250ml of solution to 1 L with water. Alternatively, an electroless coppersolution can be prepared by mixing Enplate Cu-700A (6% by volume),Enplate Cu-700B (6% by volume), Enplate Cu-700C (2.25% by volume), andwater. Fourth, and finally, the assembly surface is electroplated with ametal aside from nickel or copper, such as silver. Optionally, themetal-plated assembly surface may then be baked to further harden themetal coating. At the conclusion of the metal plating process, a metalcoating will have been applied to the assembly surface, includingbondlines of adhesives formulated in the practice of the invention,thereby providing the assembly with a highly conductive surface.

The adhesives of the invention enable one to bond together cyanate estercomposite articles into a single assembly without experiencing theabsence of plating on the adhesive bondlines. Thus, by employing thepresent adhesives, the resulting assembly of cyanate ester compositearticles exhibits complete coverage by subsequently plated metals.Moreover, the adhesion between the subsequently-plated metals and theadhesive bondlines, like that between the metals and the cyanate estercomposites, is generally very good according to ASTM method D3359Bperformance standards, as discussed in detail in the examples below.

EXAMPLES

To demonstrate the benefits achieved in the practice of the invention,three series of adhesives were formulated and tested. More specifically,a series of epoxy adhesives and a series of cyanate ester adhesives wereformulated as reported in Tables I and II below, respectively, forcomparison to adhesives formulated in accordance with the invention,which are reported in Table III. In each table, the adhesives have theformulations indicated in the second column of the table.

In general, all of the example adhesives were prepared by combining thereported ingredients and mixing until a thoroughly wetted mass wasachieved having the consistency of flowable paste. The adhesive mixtureswere degassed prior to application to the substrate. With particularregard to the adhesives of Table III, an attempt was made to produce thecyanate ester powder by curing the cyanate ester material then freezingit in liquid nitrogen before grinding into a fine powder using anOsterizer blender. The ground materials were then passed through meshnos. 104, 200, and 325 sieves and separated into 106 μm, 74 μm, and 45μm sizes, respectively. The yields were very small from the screeningprocess, especially for the 45 μm size, even though repeated numeroustimes. Thus, the blender did not achieve sufficient particle-sizereduction.

To achieve sufficient particle-size reduction to less than about 25 μm,a more aggressive process was conducted in which the cast materials werefirst subjected to pre-crushing and then cryogenic (-300° F.) milling.The milling was conducted 20 times at 20,000 rpm centrifugal force, andthe particles were then classified to yield 75 μm and 25 μm sizes.

The prepared adhesives were applied to either coupons of cured cyanateester composite or occasionally to G-10 for economic reasons duringearly screening trials. More specifically, panels comprising a cyanateester resin and graphite fibers were cured using conventional curecycles as specified by the vendor of the composite. The panels were thencut into plating coupons measuring about 1 inch×1 inch×0.02 inch. Thecoupons were masked twice with 3M Scotch brand A11280 tapes with asquare-shaped hole in the center. The square surface of the cyanateester composite coupons were abraded and solvent wiped prior to theadhesive bonding. The square patch of the adhesive applied to thecoupons was approximately 0.53 inch×0.53 inch×0.008 inch.

The adhesives were allowed to cure at room temperature (although a fewwere cured at 150° F. as indicated) at cure times specified for eachformulation in the tables. The coupons were cured with the adhesivepatches either exposed to air at room temperature, against Teflon™lamination at room temperature, against mold-released coated stainlesssteel, or in an oven at elevated temperatures. After cure, the maskedtapes were removed and the coupons were labeled accordingly. The curedadhesive-coated coupons were then etched using a two-step processwherein the coupon surface was first immersed in a relatively aggressiveprimary amine followed by immersion in a relatively nonaggressiveprimary amine.

The etched adhesive coating was then plated with a first layer of copperfollowed by a second layer of silver. More particularly, theadhesive-coated coupons surfaces were first cleaned with acidicsolutions then plated with copper by immersion in an electroless platingsolution and finally electroplated with silver.

Thereafter, the adhesion between the adhesive-coated panel surface andthe metal plating was determined in accordance with a modified versionof ASTM method D3359 "Test Method B--Cross-Cut Tape Test" (hereinafter"ASTM method D3359B") which is specifically used to assess the adhesionof coating films to metallic substrates by applying and removingpressure-sensitive tape over cuts made in the film. In the standardD-3359 tape test, a cross-hatch pattern (about 1 inch×1 inch) is scribedthrough the metallic plating with a razor sharp instrument. To thissurface a pressure sensitive tape with an adhesion of 40 to 45oz./in.-width is applied and peeled. Depending upon how many squares ofplating are removed from the substrate by peeling the tape, a numericalrating is ascribed to the test. The best adhesion rating is a "5", whichis designated when no plating is removed from the surface during thepeel.

Rather than employ tapes having adhesion ranging from 40 to 45oz./in.-width as specified in ASTM D-3359, a range of pressure-sensitivetapes were employed that had been calibrated to various levels ofplating adhesion. More particularly, pressure-sensitive tapes werecalibrated beginning at 45 oz./in.-width up to 150 oz./in.-width platingadhesions. As such, this modified ASTM D-3359 test is more aggressivethan the standard ASTIM D-3359 test described above. With specificregard to the adhesives reported in Table III, their adhesiveness wastested with 150 oz./in.-width tape.

In addition to the above-described adhesion test for the adhesive patch,a modified form of ASTM D-3359 was performed to test the thin bondlineadhesion. The cross-hatch pattern associated with the thin bondline testwas much smaller than the above-described test: the bondline test wascross-hatched over an area of about 1 inch×0.03 inch. As a result, onlyseven of the cross hatch squares straddled the bondline. Part of thesquares were on the plated graphite cyanate ester coupons on either sideof the butt joint. The following scoring system for adhesion was adoptedfor the cross-hatched plating on the bondline after the tapes werepulled:

5=perfect adhesion

4=slight delamination along the edges of the cut

3=a surface area equal to one full square of plating was removed

2=two squares of plating removed

1=three squares of plating removed

0=more than half of the cross-hatch region removed

It is noted that bondline adhesion is generally higher than adhesion toa large patch of adhesive.

Referring now to Table I, the epoxy-based adhesives without cyanateester filler are presented. On the whole, the epoxy adhesiveformulations show poor plating and poor adhesion. Within 79 formulationtrials, only the following formulations had good adhesion with the 150oz./in.-width tape using ASTM D3359 on entire patches of resin: B. F.Goodrich 1177 (formulation no. 12), B. F. Goodrich 1273 (formulationnos. 17 and 18), Epiphen 825 filled with CAT-119 (formulation no. 14),Hysol 9395 (formulation no. 16), and Hysol 9394 (formulation no. 15).However, these results were anomalous, since a retesting showed noadhesion for all these formulations at only 20 oz./in.-width tape.Therefore, it is concluded that none of the epoxy adhesive formulationsin Table I can be reliably plated on patches of pure resin.

With regard to the cyanate ester adhesives of Table II, these adhesivesexhibit good etching and plating but show poor adhesion strengths. Thetackiness of the specimens indicates that the pure cyanate esteradhesives were not completely cured. Cure temperatures of 200° F. provedto be insufficient to properly cure the cyanate ester adhesives, whichinstead remained tacky to the touch. In practice, the minimumtemperatures to cure E083194-1M and EX-1502 are 250° F. for three hourswhile BTCy-1 and EX-1515 require a cure temperature of 350° F. for abouttwo hours.

Referring to Table III, therein are reported adhesives formulated inaccordance with the present invention. In general, adhesives formulatedin accordance with the invention exhibit adhesion ratings of "5" at 150oz./in.-width using ASTM D3359. One exception was when a TEPA- orTETA-cured adhesive is cured against Teflon™ surfaces. Morespecifically, the cure for TEPA- and TETA-cured adhesives in air withoutbeing against any surfaces such as steel or Teflon™ remains tacky.However, these TEPA- and TETA-based adhesives were laminated andnon-tacky when cured against steel or Teflon™. This is not a result ofinteraction with the atmosphere, as it also occurs in a nitrogenenvironment. It seems to be a surface chemistry phenomenon. The problemis complicated, as it has been shown empirically that it is related tothe interaction of the amine curative and the cyanate ester filler.

The examples of Table III clearly show the need to employ a particlesize of less than about 25 μm for the cyanate ester powder filler,examples that employed a particle size of about 45 μm repeatedly hadless plating adhesion. Therefore, although grinding the cyanate esterpolymer into fine powder having a particle size of less than about 25 μmis technically challenging, it was imperative to the quality ofadhesion.

Room temperature cure provides the best plating adhesion. Curing theepoxy at elevated temperatures increases the amount of cross-linking ofthe polymer and makes the epoxy more difficult to etch with the amine.Since the cyanate ester filler tends to be coated with epoxy, andbecause there is not enough surface texturing, not enough filler isetched away. Thus, a room temperature cure provides the strongest amineattack and the best surface texturing for surface adhesion afteretching.

The experimental data in Table III illustrates that BTCy-1 fillerprovides the best results in etching and plating of the cyanate esterpolymers tested, and particularly showed the smoothest texture after theprocess. The cyanate ester powders ranging from best performance toworst performance according to this experimental data are as follows:BTCy-1, E083194-1M, EX-1502, and EX-1515.

Finally, both EPON 815 and EPON 828 epoxy adhesives showed acceptablequalities. EPON 815 and EPON 828 primary differ in their viscosities:EPON 815 has a lower viscosity that was more easily mixed with cyanateester powder.

                                      TABLE I                                     __________________________________________________________________________    Epoxy Adhesive Formulation                                                                          Total Cure                                                                         Plating                                                                             ASTM D3359 Tape Test                                         Cure Condi-                                                                         Time Texture                                                                             Patch                                                                              Bondline                                ID #                                                                             Formulation  tion  (R.T.)                                                                             (Graininess)                                                                        (oz) (oz)                                    __________________________________________________________________________    1  100 g Epon 815                                                                             Exposed in                                                                          7 days                                                                             5          2+                                         3 g Cabosil  air                   (90 oz)                                    12 g TETA                                                                  2  50 g (67%)Epon                                                                             Exposed in                                                                          3 days                                                                             4          2+                                         g 15         air                   (90 oz)                                    25 g (33%) Graphite                                                           130E                                                                          6 g TETA                                                                   3  Hysol 9395 A&B                                                                             Exposed in                                                                          8.5 days                                                                           5          5-                                         15% Cat 119  air                   (135 oz)                                4  Hysol 9394 A&B                                                                             Exposed in                                                                          7.5 days                                                                           5          5-                                                      air                   (135 oz)                                5  BF Goodrich 1177                                                                           Exposed in                                                                          8.5 days                                                                           5          2                                          A&B          air                   (135 oz)                                6  100 g Epon 815*                                                                            Exposed in                                                                          2 days                                                                             5     0    5-*                                        12 g TETA    air              (45 oz)                                                                            (135 oz)                                7  HysoI 9395 A&B                                                                             Exposed in                                                                          68 hrs                                                                             5          3                                          15% Cat 119  air                   (90 oz)                                 8  Hysol 9394 A&B                                                                             Exposed in                                                                          42 hrs                                                                             5          4                                                       air                   (90 oz)                                 9  B. F. Goodrich 1177                                                                        Exposed in                                                                          67 hrs                                                                             5          3-                                         A&B          air                   (90 oz)                                 10 Epiphen 825 Kit                                                                            Exposed in                                                                          66 hrs                                                                             5          1+                                         15% Cat 119  air                   (90 oz)                                 11 B. F. Goodrich 1177                                                                        Exposed in                                                                          2 weeks                                                                            5     0                                               A&B          air              (70 oz)                                                      200° C./2 hr                                           12 B.F. Goodrich 1177                                                                         Exposed in                                                                          3 days                                                                             5     0    3                                          A&B          air              (20 oz)                                                                            (150 oz)                                13 B. F. Goodrich 1177                                                                        200° C./1 hr                                                                 3 days                                                                             4     0    0                                          A&B                           (20 oz)                                                                            (45 oz)                                 14 Epiphen 825 Kit                                                                            Exposed in                                                                          1 days                                                                             5     0    4                                          15% Cat 119  air              (20 oz)                                                                            (150 oz)                                15 Hysol 9394 A&B                                                                             Exposed in                                                                          1 days                                                                             4     0    3                                                       air              (20 oz)                                                                            (150 oz)                                16 Hysol 9395 A&B                                                                             Exposed in                                                                          1 day                                                                              4     0    4                                          15% Cat 119  air              (20 oz)                                                                            (150 oz)                                17 B. F. Goodrich 1273                                                                        Exposed in                                                                          1 day                                                                              3     0    2                                          A&B          air              (20 oz)                                                                            (150 oz)                                18 B. F. Goodrich 1273                                                                        200° C./1 hr                                                                 1 day                                                                              5     0    0                                          A&B                           (20 oz)                                                                            (90 oz)                                 19 25 g Epiphen 825                                                                           100° C./1 hr                                                                      3     0                                               3 g Modifier                  (45 oz)                                         10 g Mica                                                                     4 g Converter                                                              20 25 g Epiphen 825                                                                           100° C./1 hr                                                                      3     0                                               3 g Modifier                  (45 oz)                                         10 g CaCO.sub.3                                                               4 g Converter                                                              21 25 g Epiphen 825                                                                           100° C./1 hr                                                                      5     0                                               3 g Modifier                  (45 oz)                                         20 g CaCO.sub.3                                                               4 g Converter                                                              22 25 g Epiphen 825                                                                           100° C./1 hr                                                                      5     0                                               3 g Modifier                  (45 oz)                                         30 g CaCO.sub.3                                                               4 g Converter                                                              23 25 g Epiphen 825   2 days                                                                             5     0                                               3 g Modifier                  (45 oz)                                         Fluidized CaCO.sub.3                                                          4 g Converter                                                              24 25 g Epiphen 825                                                                           100° C./2 hr                                                                      2     0                                               3 g Modifier                  (45 oz)                                         10 g Mica 4×                                                            4 g Converter                                                              25 25 g Epiphen 825                                                                           100° C./2 hr                                                                      5     0                                               3 g Modifier                  (45 oz)                                         10 g Rubber Particles                                                         4 g Converter                                                              26 25 g Epiphen 825   2 days                                                                             5     0                                               3 g Modifier                  (45 oz)                                         10 g Mica 4×                                                            4 g Converter                                                              27 25 g Epiphen 825   2 days                                                                             3     0                                               3 g Modifier                  (45 oz)                                         10 g Rubber Particles                                                         4 g Converter                                                              28 25 g Epiphen 825                                                                           100° C./1 hr                                                                      3     0                                               3 g Modifier                  (45 oz)                                         10 g Mica                                                                     4 g Converter                                                              29 25 g Epiphen 825                                                                           100° C./1 hr                                                                      4     0                                               3 g Modifier                  (20 oz)                                         10 g CaSO.sub.4 (4.0 μm)                                                   4 g Converter                                                              30 25 g Epiphen 825   1 day                                                                              5     2                                               3 g Modifier                  (45 oz)                                         10 g CaSO.sub.4 (4.0 μm)                                                   4 g Converter                                                              31 25 g Epiphen 825                                                                           100° C./1 hr                                                                      4     0                                               3 g Modifier                  (20 oz)                                         Fluidized CaCO.sub.3 (for                                                     1 min)                                                                        4 g Converter                                                              32 25 g Epiphen 825   1 day                                                                              3     0                                               3 g Modifier                  (20 oz)                                         Fluidized CaCO.sub.3 (for 1 min)                                              4 g Converter                                                              33 25 g Epiphen 825                                                                           100° C./1 hr                                                                      4+    0                                               3 g Modifier                  (20 oz)                                         Fluidized CaCO.sub.3 (for                                                     2 min)                                                                        4 g Converter                                                              34 25 g Epiphen 825                                                                           100° C./1 hr                                                                      4     0                                               3 g Modifler                  (20 oz)                                         Fluidized CaCO.sub.3 (for                                                     5 min)                                                                        4 g Converter                                                              35 25 g Epiphen 825   1 day                                                                              5     0                                               3 g Modifier                  (20 oz)                                         Fluidized CaCO.sub.3 (for 8 min)                                              4 g Converter                                                              36 25 g Epiphen 825   1 day                                                                              NT    0                                               3 g Modifier                  (20 oz)                                         Sprayed CaCO.sub.3                                                            4 g Converter                                                              37 38 g DEN 438 100° C./1 hr                                                                      4+    0                                               5.75 g Epon 862               (20 oz)                                         6.25 g Heloxy 58005                                                           10 g 75% DEEA. 25%                                                            DETA                                                                       38 38 g DEN 438 100° C./1 hr                                                                      4+    0                                               5.75 g Epon 862               (20 oz)                                         6.25 g Heloxy 58006                                                           10 g 75% DEEA, 25%                                                            DETA                                                                       39 20 g DEN 438 100° C./1 hr                                                                      4+    0                                               5 g Heloxy 5048               (20 oz)                                         10 g Mica 4×                                                            3 g ATBN 1300 × 6                                                       4 g 75% DEEA, 25%                                                             DETA                                                                       40 38 g DEN 438       1 day                                                                              4-    0                                               5.75 g Epon 862               (45 oz)                                         6.25 g Heloxy 58005                                                           10 g 75% DEEA, 25% DETA                                                    41 38 g DEN 438       1 day                                                                              5     1                                               5.75 g Epon 862               (45 oz)                                         6.25 g Heloxy 55006                                                           10 g 75% DEEA, 25% DETA                                                    42 20 g DEN 438       1 day                                                                              5     0                                               5 g Heloxy 5048               (45 oz)                                         10 g Mica 4×                                                            3 g ATBN 1300 × 6                                                       4 g 75% DEEA, 25% DETA                                                     43 50 g Hysol EA9395                                                                          100° C./1 hr                                                                      4     0                                               part A                        (20 oz)                                         8.5 g Hysol EA9395                                                            part B                                                                     44 50 g Hysol EA9395 part A                                                                         1 day                                                                              5     0                                               8.5 g Hysol EA9395 part B     (20 oz)                                      45 25 g DEN 438 100° C./1 hr                                                                      3     0                                               25 g Heloxy 58598             (20 oz)                                         5 g 50% DEEA, 50%                                                             DETA                                                                       46 388 DEN 438  100° C./1 hr                                                                      4+    0                                               5.75 g Epon 862               (20 oz)                                         6.25 g Heloxy 58005                                                           5 g 50% DEEA, 50%                                                             DETA                                                                       47 38 g DEN 438 100° C./1 hr                                                                      4+    0                                               5.75 g Epon 862               (20 oz)                                         6.25 g Heloxy 58006                                                           5 g 50% DEEA, 50%                                                             DETA                                                                       48 25 g DEN 438       1 day                                                                              3-    3                                               25 g Heloxy 58598             (45 oz)                                         5 g 50% DEEA. 50% DETA                                                     49 38 g DEN 438       1 day                                                                              5     1                                               5 .7S g Epon 862              (45 oz)                                         6.25 g Heloxy 58005                                                           50% DEEA, 50% DETA                                                         50 38 g DEN 438       1 day                                                                              4     0                                               5.75 g Epon 862               (20 oz)                                         6.25 g Heloxy 58006                                                           50% DEEA. 50% DETA                                                         51 B. F. Goodrich 1177                                                                        100° C./1 hr                                                                      3-    0                                               A&B                           (20 oz)                                      52 B. F. Goodrich 1177                                                                              1 day                                                                              4     5                                               A&B                           (150 oz)                                     53 B. F. Goodrich 1273                                                                        100° C./1 hr                                                                      4     0                                               A&B                           (20 oz)                                      54 B. F. Goodrich 1273                                                                              1 day                                                                              4     5                                               A&B                           (150 oz)                                     55 B. F. Goodrich 1177 A&B                                                                          1 day                                                                              4     5                                               10% Cat 119                   (150 oz)                                     56 B. F. Goodrich 1177 A&B                                                                          1 day                                                                              4     5                                               20% Cat 119                   (150 oz)                                     57 B. F. Goodrich 1273 A&B                                                                          1 day                                                                              4     5                                               10% Cat 119                   (150 oz)                                     58 B. F. Goodrich 1273 A&B                                                                          1 day                                                                              4     3                                               20% Cat 119                   (150 oz)                                     59 25 g Epiphen 825   1 day                                                                              3-    5                                               3 g Modifier                  (150 oz)                                        2.5 g Cat 119                                                                 4 g Converter                                                              60 25 g Epiphen 825   1 day                                                                              3-    4                                               3 g Modifier                  (150 oz)                                        5.0 g Cat 119                                                                 4 g Converter                                                              61 50 g Hysol EA9395 part A                                                                         1 day                                                                              4     5                                               8.5 g Hysol EA9395 part B     (150 oz)                                        5.0 g Cat 119                                                              62 50 g Hysol EA9395 part A                                                                         1 day                                                                              4     5                                               8.5 g Hysol EA9395 part B     (150 oz)                                        10 g Cat 119                                                               63 50 g Hysol EA9323 part A                                                                         2 days                                                                             3     0                                               50 g Hysol EA9323 part B      (20 oz)                                      64 50 g Hysol EA9323 part A                                                                         1 day                                                                              4     0                                               50 g Hysol EA9323 part B      (20 oz)                                         10% Cat 119                                                                65 50 g Hysol EA9323 part A                                                                         1 day                                                                              4     1                                               50 g Hysol EA9323 part B      (150 oz)                                        20% Cat 119                                                                66 3M 2214NMF   100° C./1 hr                                                                 4 days                                                                             4     0                                                            121° C./  (20 oz)                                                      3.5 hr                                                        67 50 g 3M 2214NMF                                                                            100° C./1 hr                                                                 4 days                                                                             4     0                                               10% Cat 119  121° C./  (20 oz)                                                      3.5 hr                                                        68 50 g 3M 2214NMF                                                                            100° C./1 hr                                                                 4 days                                                                             4     0                                               20% Cat 119  121° C.   (20 oz)                                                      3.5 hr                                                        69 50 g Hysol EA9394 part A                                                                         1 day                                                                              4     4                                               8.5 g Hysol EA9394 part B     (150 oz)                                     70 50 g Hysol EA9394 part A                                                                         1 day                                                                              4     4                                               8.5 g Hysol EA9394 part B     (150 oz)                                        10% Cat 119                                                                71 50 g Hysol EA9394 part A                                                                         1 day                                                                              4     4                                               8.5 g Hysol EA9394 part B     (150 oz)                                        20% Cat 119                                                                72 50 g Hysol EA9396 part A                                                                         1 day                                                                              3-    1                                               15 g Hysol EA9396 part B      (150 oz)                                     73 50 g Hysol EA9396  1 day                                                                              4     3                                               part A                        (150 oz)                                        15 g Hysol EA9396                                                             part B                                                                        10% Cat 119                                                                76 Hysol 1-C          1 day                                                                              4     0                                               10% Cat 119                   (150 oz)                                        1% Epoxy Silane                                                            77 Hysol 1-C          1 day                                                                              4     0                                               20% Cat 119                   (150 oz)                                        1% Epoxy Silane                                                            78 Hysol 1-C          1 day                                                                              4     3                                               10% Cat 119                   (150 oz)                                     79 Hysol 1-C          1 day                                                                              4     3                                               20% Cat 119                   (150 oz)                                     __________________________________________________________________________

                                      TABLE II                                    __________________________________________________________________________    Cyanate Ester Adhesive Formulation                                                         Total Cure                                                                           Tackiness                                                                            Plating                                                    Cure Time   (exposed                                                                             Texture                                                                             ASTM D3359 Tape Test                         Formulation                                                                           Condition                                                                          (R.T.) side)  (Graininess)                                                                        90 oz                                                                            135 oz                                                                            150 oz                                __________________________________________________________________________    Bryte 083194-1M                                                                       200° C./                                                                           slightly tacky                                                                       5     2                                            10% cat 119                                                                           1.5 hr                                                                Bryte 1502                                                                            225° C./                                                                           tacky  5     4                                                    3 hr                                                                  E083194-1M                                                                            200° F./                                                                           slightly tacky                                                                       5     1+                                           10% cat 119                                                                           1.5 hrs                                                               EX 1502 225° F./                                                                           tacky  5     4+                                                   3 hrs                                                                 E083194-1M                                                                            175° F./                                                                           tacky  5            4                                             7.5 hrs                                                               E083194-1M                                                                            150° F./                                                                           tacky  5            2+                                            17 hrs                                                                EX 1502 225° F./                                                                           tacky  3            3                                             3 hrs                                                                 EX 1502 200° F./                                                                           tacky  3            2                                             4 hrs                                                                 E083194-1M                                                                            200° F./                                                                           tacky  4        3+                                                1.5 hrs                                                               E083194-1M                                                                            200° F./                                                                           slightly tacky                                                                       4        5                                         10% cat 119                                                                           1.5 hrs                                                               E083194-1M                                                                            200° F./                                                                           slightly tacky                                                                       3        3                                         20% cat 119                                                                           1 hr                                                                  E083194-1M                                                                            175° F./                                                                           tacky  4        4+                                                3.5 hrs                                                               E083194-1M                                                                            130° F./                                                                           tacky  4        1                                                 15 hrs                                                                EX 1502 250° F./                                                                           tacky  4        0                                                 1.5 hrs                                                               E083194-IM                                                                            200° F./                                                                           slightly tacky                                                                       4        4                                         20% cat 119                                                                           3.5 hrs                                                               EX 1502 250° F./                                                                    16 hrs tacky  4            4                                             3.5 hr                                                                E083194-IM                                                                            200° F./                                                                    16 hrs tacky  3-           1                                             3.5 hrs                                                               __________________________________________________________________________

                                      TABLE III                                   __________________________________________________________________________    Epoxy - Cyanate Ester (powder) Formulation                                                                           ASTM D3359                                                                    Tape Test                                                   Total Cure                                                                         Tackiness                                                                            Plating                                                                             (150 oz)                                             Cure   Time (exposed                                                                             Texture  Bond                                Formulation   Condition                                                                            (R.T.)                                                                             side)  (graininess)                                                                        Patch                                                                            Line                                __________________________________________________________________________    1.5 g Epon 8l5                                                                              Against steel                                                                        20 days                                                                            non-tacky                                                                            5     5-                                     0.50 g CE powder BTCy-1 (25                                                                 coated with laminated                                           μm)        EF-179                                                          0.18 g TEPA                                                                   1.5 g Epon 815                                                                              Against steel                                                                        20 days                                                                            non-tacky                                                                            4     5                                      0.50 g CE powder 083194-1M                                                                  coated with laminated                                           (25 μm)    EF-179                                                          0.18 g TEPA                                                                   1.5 g Epon 815                                                                              Against steel                                                                        20 days                                                                            non-tacky                                                                            4     4+                                     0.50 g CE powder EX1515 (25                                                                 coated with laminated                                           μm)        EF-179                                                          0.18 g TEPA                                                                   1.5 g Epon 828                                                                              Against steel                                                                        20 days                                                                            non-tacky                                                                            3     5                                      0.50 g CE powder BTCy-1 (25                                                                 coated with laminated                                           μm)        EF-179                                                          0.18 g TEPA                                                                   1.5 g Epon 828                                                                              Exposed in air                                                                       21 days                                                                            slightly tacky                                                                       4     5                                      0.50 g CE powder BTCy-1 (25                                                   μm)                                                                        0.18 g TEPA                                                                   1.5 g Epon 828                                                                              Exposed in air                                                                       21 days                                                                            tacky  3     5                                      0.50 g CE powder 083194-1M                                                    (25 μm)                                                                    0.18 g TEPA                                                                   1.5 g Epon 828                                                                              Exposed in air                                                                       21 days                                                                            very tacky                                                                           4     5                                      0.50 g CE powder EX1515 (25                                                   μm)                                                                        0.18 g TEPA                                                                   1.5 g Epon 815                                                                              Exposed in air                                                                       6 days                                                                             tacky  4     5                                      0.50 g CE powder BTCy-1 (25                                                   μm)                                                                        0.18 g TEPA                                                                   1.5 g Epon 815                                                                              Against Teflon                                                                       6 days                                                                             non-tacky                                                                            4     0                                      0.50 g CE powder BTCy-1 (25                                                                             Iaminated                                           μm)                                                                        0.18 g TEPA                                                                   1.5 g Epon 815                                                                              Exposed in air                                                                       7 days                                                                             tacky  4     5                                      0.50 g CE powder EX1515 (25                                                   μm)                                                                        0.18 g TEPA                                                                   1.5 g Epon 815                                                                              Against Teflon                                                                       7 days                                                                             non-tacky                                                                            4     0                                      0.50 g CE powder EX 1515 (25                                                                            Iaminated                                           μm)                                                                        0.18 g TEPA                                                                   1.5 g Epon 815                                                                              150° F./2 hrs                                                                 7 days                                                                             slightly tacky                                                                       4     0                                      0.50 g CE powder EX1515                                                       (25 μm)                                                                    0.18 g TEPA                                                                   1.5 g Epon 815                                                                              Exposed in air                                                                       8 days                                                                             tacky  4     5                                      0.50 g CE powder 083194-1M                                                    (25 μm)                                                                    0.18 g TETA                                                                   1.5 g Epon 815                                                                              Against Teflon                                                                       8 days                                                                             non-tacky                                                                            4     0                                      0.50 g CE powder 083194-1M                                                                              laminated                                           (25 μm)                                                                    0.18 g TETA                                                                   1.5 g Epon 815                                                                              150° F./2 hrs                                                                 7 days                                                                             slightly tacky                                                                       3     2+                                     0.50 g CE powder 083194-1M                                                    (25 μm)                                                                    0.18 g TETA                                                                   1.5 g Epon 815                                                                              150° F./2 hrs                                                                 7 days                                                                             slightly tacky                                                                       3     0                                      0.50 g CE powder BTCy-1 (25                                                   μm)                                                                        0.18 g TETA                                                                   1.5 g Epon 815                                                                              Exposed in air                                                                       5 days                                                                             tacky  4     5                                      0.50 g CE powder EX1515 (25                                                   μm)                                                                        0.18 g TETA                                                                   1.5 g Epon 815                                                                              Against Teflon                                                                       8 days                                                                             non-tacky                                                                            4     3                                      0.50 g CE powder EX1515 (25                                                                             laminated                                           μm)                                                                        0.18 g TETA                                                                   2.0 g Epon 815                                                                              bondline ex-                                                                         4 days                                                                             tacky  3     4+ 4                                   1.0 g CE powder 083194-1M                                                                   posed to air,                                                   (45 μm)    patch against                                                   0.24 g TETA   Teflon                                                          0.50 g Epon 8l5                                                                             Exposed to air                                                                       4 days                                                                             tacky  3-    2                                      0.50 g Epon 828                                                               0.50 g CE powder EX1502 (45                                                   μm)                                                                        0.12 g TETA                                                                   0.50 g Epon 815                                                                             Against Teflon                                                                       4 days                                                                             non-tacky                                                                            2     3-                                     0.50 g Epon 828           laminated                                           0.50 g CE powder EX1502 (45                                                   μm)                                                                        0.12 g TETA                                                                   0.50 g Epon 815                                                                             Exposed to air                                                                       4 days                                                                             tacky  4     4+                                     0.50 g Epon 828                                                               0.50 g CE powder BTCy-1 (45                                                   μm)                                                                        0.12 g TETA                                                                   0.50 g Epon 815                                                                             Against Teflon                                                                       4 days                                                                             non-tacky                                                                            3     1                                      0.50 g Epon 828           laminated                                           0.50 g CE powder BTCy-1 (45                                                   μm)                                                                        0.12 g TETA                                                                   1.0 g B.F. Goodrich 1177A&B                                                                 Exposed to air                                                                       7 days                                                                             slightly tacky                                                                       5     5                                      0.50 g CE powder EX1502 (45                                                   μm)                                                                        1.0 g B.F. Goodrich 1177A&B                                                                 Against Teflon                                                                       7 days                                                                             non-tacky                                                                            5     0                                      0.50 g CE powder EX1502 (45                                                                             laminated                                           μm)                                                                        1.0 g B.F. Goodrich 1177A&B                                                                 Exposed to air                                                                       7 days                                                                             slightly tacky                                                                       5     5                                      0.50 g CE powder BTCy-1 (45                                                   μm)                                                                        1.0 g B.F. Goodrich 1177A&B                                                                 Against Teflon                                                                       7 days                                                                             non-tacky                                                                            5     0                                      0.50 g CE powder BTCy-1 (45                                                                             laminated                                           μm)                                                                        1.0 g Epon 815                                                                              Exposed to air                                                                       6 days                                                                             slightly tacky                                                                       4     4+                                     0.50 g Epon 828                                                               0.50 g CE powder BTCy-1 (45                                                   μm)                                                                        0.18 g TETA                                                                   1.0 g Epon 815                                                                              Against Teflon                                                                       6 days                                                                             non-tacky                                                                            4     4                                      0.50 g Epon 828           laminated                                           0.50 g CE powder BTCy-1 (45                                                   μm)                                                                        0.18 g TETA                                                                   0.50 g Epon 815                                                                             Exposed to air                                                                       5 days                                                                             tacky  3     1+                                     0.50 g Epon 828                                                               0.50 g CE powder EX1515 (45                                                   μm)                                                                        0.12 g TETA                                                                   0.50 g Epon 815                                                                             Against Teflon                                                                       5 days                                                                             non-tacky                                                                            2     2-                                     0.50 g Epon 828           laminated                                           0.50 g CE powder EX1515 (45                                                   μm)                                                                        0.12 g TETA                                                                   1.0 g B.F. Goodrich 1177A&B                                                                 Against Teflon                                                                       7 days                                                                             slightly tacky                                                                       3     1+                                     0.50 g CE powder BTCy-1(45                                                    μm)                                                                        1.0 g Epon 815                                                                              Exposed to air                                                                       5 days                                                                             slightly tacky                                                                       3     3+                                     0.50 g Epon 828                                                               0.50 g CE powder EX1515 (45                                                   μm)                                                                        0.18 g TETA                                                                   1.25 g Epon 815                                                                             Against Teflon                                                                       4 days                                                                             non-tacky                                                                            4     5                                      0.25 g CE powder BTCy-1 (45                                                                             laminated                                           μm)                                                                        0.25 g TETA                                                                   0.75 g Epon 815                                                                             Exposed to air                                                                       4 days                                                                             slightly tacky                                                                       3     0                                      0.50 g Epon 828                                                               0.25 g CE powder BTCy-1 (45                                                   μm)                                                                        0.25 g TETA                                                                   0.75 g Epon 815                                                                             Against Teflon                                                                       4 days                                                                             non-tacky                                                                            4     5                                      0.50 g Epon 828           laminated                                           0.25 g CE powder BTCy-1 (45                                                   μm)                                                                        0.25 g TETA                                                                   __________________________________________________________________________

Accordingly, it has been demonstrated that an adhesive formulated inaccordance with the invention is successfully plated with metals afterhaving been subjected to surface texturing.

INDUSTRIAL APPLICABILITY

The adhesives of the invention are expected to be successfully employedin industries involving the metal plating of custom formulated plasticparts. Particularly, the adhesives of the invention are expected to findutility in such industrial applications as the manufacture ofautomobiles, motorhomes, aircraft, boats, and manufactured homes.

Thus, there has been disclosed an adhesive for bonding cyanate estercomposites together, with the adhesive capable of adhering tosubsequently-plated metal after having been etched in a surfacetexturing process. Moreover, a method of formulating the presentadhesive formulations is provided as well as a method for bondingcyanate ester composite articles with the present adhesives. It will bereadily apparent to those of ordinary skill in this art that variouschanges and modifications of an obvious nature may be made withoutdeparting from the spirit of the invention, and all such changes andmodifications are considered to fall within the scope of the invention,as defined by the appended claims.

What is claimed is:
 1. A method for bonding cyanate ester compositearticles to one another, said cyanate ester composite articles eachhaving a surface, said method comprising:(a) preparing an adhesiveaccording to steps comprising:(i) providing a cured cyanate esterpolymer in powder form; and (ii) mixing said cured cyanate ester polymerwith a polymer mixture to form a thoroughly wetted mass, said polymermixture comprising at least one polyepoxide resin and a substantiallystoichiometric amount of curing agent. (b) applying said adhesive tosaid surface of at least one of said cyanate ester composite articles tobe bonded; (c) positioning said cyanate ester composite articles to forma mated assembly, said adhesive therebetween and in contact with each ofsaid cyanate ester composite articles; and (d) allowing said adhesive tocure, thereby bonding said cyanate ester composite articles to oneanother.
 2. The method of claim 1 further comprising a step (b')following said step (a) and preceding said step (b), step (b')comprising freezing said adhesive for storage and thereafter thawingsaid frozen adhesive for use.
 3. The method of claim 1 wherein said atleast one polyepoxide resin has a viscosity not exceeding about 30,000cP at room temperature and is selected from the group consisting ofdiglycidyl ethers of Bisphenol A and diglycidyl ethers of Bisphenol F.4. The method of claim 3 wherein said at least one polyepoxide resin isselected from the group consisting of (a) a mixture comprising 11% butylglycidyl ether and 89% diglycidyl ether of Bisphenol A, said mixturehaving an epoxy equivalent weight within the range of about 175 to 195,and (b) diglycidyl ether of Bisphenol A having an epoxy equivalentweight within the range of about 185 to
 192. 5. The method of claim 1wherein said curing agent comprises at least one aliphatic polyamine andoptionally further comprises at least one catalytic curing agent.
 6. Themethod of claim 5 wherein said at least one aliphatic polyamine isselected from the group consisting of triethylenetetramine andtetraethylenepentamine and said at least one catalytic curing agent isselected from the group consisting of tris (dimethyl-amino) methylphenol and amine-terminated butadiene-nitrile rubber.
 7. The method ofclaim 1 wherein said filler is present in said adhesive in an amountranging from about 15 to 50 vol % and wherein said cured cyanate esterpolymer is in powder form comprising nominally spheroidal particleshaving an average diameter of less than about 25 μm.
 8. A method forforming and plating an assembly of cyanate ester composite articles,each of said cyanate ester composite articles having a surface, saidmethod comprising the steps of(a) preparing an adhesive according to thesteps comprising:(i) providing a cured cyanate ester polymer in powderform; and (ii) mixing said cured cyanate ester polymer with a polymermixture to form a thoroughly wetted mass, said polymer mixturecomprising at least one polyepoxide resin and a substantiallystoichiometric amount of curing agent; (b) applying said adhesive tosaid surface of at least one of said cyanate ester composite articles tobe bonded; (c) positioning said cyanate ester composite articles to forma mated assembly, said adhesive therebetween and in contact with saidsurface of each of said cyanate ester composite articles; (d) allowingsaid adhesive to cure, thereby bonding said cyanate ester compositearticles to one another to form an assembly, said assembly having asurface; (e) chemically etching said surface of said assembly, includingany of said adhesive exposed at said surface of said assembly; and (f)plating said surface of said assembly such that said surface of saidassembly is completely covered with metal, including said adhesiveexposed at said surface of said assembly.